Email migration refers to a process of transferring emails from a mailbox in a source system to a corresponding mailbox in a target system. An email migration may be performed for various reasons including when a company switches over to a new email service provider, switches to a different platform (e.g., traditional vs. hosted), is acquired, etc. When an email migration is performed, it is typical to also migrate other content including tasks, calendar items, contacts, journals, instant messaging conversations, posted attachments, sticky notes, etc. For purposes of this specification, a migration should therefore be construed as including the transfer of email as well as other content that is oftentimes provided within an email solution. The term email should be construed to encompass not only traditional email but also other messaging formats used by group collaboration platforms that are increasingly being used in place of traditional email. For example, email should be construed to encompass group communications and their associated content within group collaboration platforms. In such cases, a group “mailbox” within a source system may be migrated to a group “mailbox” within a target system.